1. Field
The following description relates to an optical pickup device and a method of aligning light sources in an optical disc drive, and more particularly, to a grating element in an optical pickup device having a light source for multiple types of media discs.
2. Description of Related Art
In an optical pickup device, a path of a light beam from a light source and a path of a light beam reflected from a disc often overlap with each other in some section. As well known in the art, the paths overlap with each other within a section from a disc to a beam splitter, and the beam splitter splits the paths into the beam from the light source and the beam from the disc. The beam splitter causes the beam from the light source to proceed toward the disc, and causes the beam reflected from the disc to proceed toward a photodetector.
In a typical optical pickup device, a grating element is used to convert a light beam from the light source into multiple beams such as three beams. The grating element refracts a source beam from the light source to form the three beams. From among the three beams, refracted beams at opposite sides of a center beam are arranged with constant intervals. Here, the center beam is not refracted. In order to read and write to the disc, the three beams should be aligned with respect to a running track on which a laser beam is directed towards.
To align the beams, the light source and the grating element need to be arranged accurately in the optical pickup device. This arrangement is typically performed during a manufacturing processes of the optical pickup device. The arrangement is critical in an optical pickup device corresponding to multi-media, for example, an optical pickup device generating laser beams for multi-media using a single light source. An example of a multi-media light source is a twin light source that generates a laser beam for a compact disc (CD) and generates a laser beam for a digital versatile disc (DVD). The two laser beams are typically generated by separate laser chips provided in one light source.
In an optical pickup device using the twin light source, a grating element and the light source are arranged such that an intermediate location between the DVD chip and the CD chip is matched to an optical path that passes through the optical center of the grating element. When performing the alignment, relative locations and postures of the grating element and the light source are adjusted while monitoring a laser beam emitted toward an objective lens via an imaging device such as a charge-coupled device (CCD). Conventionally, only one light emitting chip, for example, the DVD chip, is aligned. This often results in a misalignment of the CD chip that is offset from the DVD chip. The misalignment denotes that an extension line between the CD chip and the DVD chip is not correctly aligned in a direction of a polarization axis of a grating element. Such a misalignment is an alignment error (hereinafter, a rotation error or a radial error) in a radial direction surrounding an optical center axis of the grating element. The rotation error needs to be corrected during manufacturing the optical pickup device.
However, because the alignment process is performed in a state where an electric current is applied to only one light emitting chip, for example, the DVD chip, only the laser beam for DVD is aligned. Accordingly, the rotation error of the extension line between the DVD chip and the CD chip may not be accurately corrected.